The present invention relates in general to valves, and in particular to a new and useful gas valve which is capable of extensively expanding the measurable range of a gas flow, by utilizing two flowmeters.
Insofar as their ability to expand measurable flow ranges by using combinations of two flowmeters and a valve, U.S. Pat. Nos. 3,677,084; 4,100,800; and 4,429,571, are examples of the prior art. These references, however are all directed to liquid flow measurements and contained a small flowmeter and a large flowmeter as part of the flowmeter packages. None of these patents describe an approach that could operate with a gas over the flow range of interest in the present invention.
Most flowmeters available commercially today operate within the maximum to minimum turn-down flow ratio of 40:1. However, a need for flowmeters with an extended operating flow range of 800:1 has been expressed, for example, by the Gas Research Institute (GRI). The gas flowmeters with extended flow range sought by GRI for residential distribution meters are expected to meet the following three specific performance requirements.
1. Turn-down ratio--about 800:1; PA1 2. Measurement accuracy--better than .+-.1%; PA1 3. Pressure drop--less than 1.0 inch of water at the maximum flow.
There are a number of commercially-available flowmeters that can meet the accuracy requirement, but no existing flowmeter or flowmeters under development currently meet all three requirements. The present invention was conceived as a means to satisfy all three requirements.